1. Field of the Invention
This invention relates to interference in radio networks and more particularly to reducing the effects of interference during communication sessions between a base station and a mobile device.
2. Description of the Related Art
As cellular and Internet communication services continue to reach into more aspects of life, mobile voice (cellular), mobile broadband data and quadruple-play (voice, data, video and mobility) multimedia services, are expected to dominate future wireless markets. All these diversified mobile broadband services share radio frequency (RF) resources. Along with the growth of mobile broadband services under limited RF resources, RF service systems are being deployed in physical proximity and share adjacent RF bands. These neighboring systems and RF equipment have an increased potential to impact each other through in-band and out of band interference. An undesired signal sourced from a neighboring RF system that exceeds certain critical levels and that is received by an RF receiver can lead to overload, intermodulation, dynamic range reduction and a noise floor rising of more than 1 dB. In the cases of dynamic range reduction, adaptive modulation schemes can be adopted to improve service performance at the receiving device, or at least, to minimize undesired link errors by reducing link capacity. This potential problem becomes progressively harder to resolve when the undesired signal is much stronger, e.g., when exceeding the desired signal by an order of magnitude, and/or the receiving device only plays a passive role within the loop of interference control.
Interference issues can be generally classified into two generic categories. One category is called inter-cell interference, and the other is called inter-system interference. Increased deployment of different wireless services in the same location and/or operating in adjacent frequency bands, can lead to increased problems with both increased inter-cell and inter-system interference.
Inter-system interference has typically been managed through RF system planning that follows Federal Communication Commission (FCC) license requirements. In addition, inter-system interference can be managed by agreement(s) negotiated among service providers. When there are only a few RF service systems deployed in the same physical location and operated in adjacent RF frequency bands, the inter-system interference is usually minor and can be managed through system planning and by negotiated service agreements. Unique interference issues can be worked out on a case-by-case basis among affected parties.
Due to diversified service growth and development in RF communications, the current approaches to managing inter-system interference may be inadequate. As RF radio bands become occupied and wireless resources become more congested, RF base stations are deployed in close proximity to each other. The RF service environment is becoming more and more traffic/interference limited. Under this tightened RF resources condition, it becomes more likely that adjacent RF service systems will operate under a power disparity environment to provide for different service requirements. When the received power at a handset or base station from an undesired signal is significantly increased, the receiving device may be overloaded, and driven into a nonlinear operating range.
For example, in the S band operation, Wireless Communication Channels (WCS) are assigned between 2.305 GHz-2.315 GHz and 2.345 GHz-2.36 GHz bands. Satellite Digital Audio Radio Services (SDARS) operators are assigned the spectrum between 2.315 GHz and 2.345 GHz and thus, WCS and SDARS operations are in adjacent frequency bands. Meanwhile, WCS base stations and SDARS ground repeaters could also be deployed to the same metropolitan area where the WCS base station transmitter is limited by 2 KW Equivalent Isotropically Radiated Power (EIRP) and SDARS ground repeater transmission can run EIRP up to 40 KW. Such an environment demonstrates a typical inter-system interference scenario including potential for overload, intermodulation, dynamic range reduction, as well as other forms of interference due to the high power disparity.
The Federal Communication Commission (FCC) spectrum auction in 700 MHz frequency range provides another potential interference scenario. For example, one-way digital video service system and 2-way mobile data service system, both running in neighboring bands of 700 MHz, could be deployed to the same metropolitan area. One-way digital video service base station transmitters can run up to 82 KW EIRP and 2-way mobile data service base station transmitters are limited to 1.6 KW EIRP. Once these two RF service systems are deployed adjacent to each other in the neighboring RF bands, a significant inter-system interference impact is possible through overload, intermodulation, dynamic range reduction as well as other forms of interference due to the high power disparity.
In addition to system planning to avoid high power disparity or otherwise plan for it, there are a variety of methods for mitigating interference impact at the device level. For example, receive filters can be used to mitigate the interference by selectively reducing the strength of the desired versus the undesired signals based, assuming the undesired signals are of different frequency. However, filters that separate signals at adjacent frequency bands can be difficult to build. Further, even when a technical solution is available, the limitations of cost and size might prevent incorporation into customer devices.
As diversified growth and development in RF communications continues, the current approaches to managing inter-system interference may be inadequate. Accordingly, improved approaches to the problems of inter-system interference are desirable.